Extraction of a plant containing an active ingredient, for example, Hydrangeae Dulcis Folium, which can be prepared by collecting and fermenting the leaves and branches of Hydrangea macrophylla SERINGE var. Thunbergii Makino followed by drying, with various solvents such as a mixture of a fat-soluble organic solvent and water affords a liquid extract containing an active ingredient such as phyllodulcin. The concentrated liquid extract, however, yields highly viscous taffy-like precipitate.
The taffy-like precipitate tends to stick to the bottom of a vessel or block a pipeline, and it is difficult to transfer to another vessel.
On the other hand, the liquid extract containing an active ingredient obtained by extraction with a solvent such as ethanol, when dried by direct drying with a spray-drier or with drum drier through no procedure for concentration, affords a very low recovery because the content of the solid component in the liquid extract is low. In addition, this operation is not a practical way because it requires special equipment such as explosion protector.
Therefore, it is difficult to produce powder highly containing an active ingredient on an industrial scale using a spray-drier or freeze drier.
On the other hand, the taffy-like precipitate is not suitable for use in foods and drinks or feeds or as raw material thereof because the directly dried precipitate is very hard.
The extract of Hydrangeae Dulcis Folium with supercritical carbon dioxide or liquidized carbon dioxide is rich in phyllodulcin as an ethanol-soluble sweetening component, which is however not easy to handle because it is in a form of paste (Japanese Published Unexamined Patent Application No. 262772/89).
As plant powder, Hydrangeae Dulcis Folium powder is exemplified, but the content of phyllodulcin in the powder is as low as 1 to 2% by weight because it is prepared by pulverizing Hydrangeae Dulcis Folium as such. Though the commercially available powder of Hydrangeae Dulcis Folium extract for use in foods and drinks is prepared by extraction of Hydrangeae Dulcis Folium with a water-soluble solvent, the content of phyllodulcin is as low as 2% by weight or less.
Thus, it is not possible to increase the content of an active ingredient in the plant powder by merely pulverizing the plant.